1. Field of the Invention
The present invention relates generally to hardfacing materials (also referred to herein as hardcoatings) that provide improved durability to tools and components to which they are applied, as well as to a system and methods for applying the protective hardcoatings to a machine or tool element that is otherwise subjected to abrasion, corrosion, erosion and/or high wear during service. The invention also relates generally to such a machine or tool element having the protective hardcoating. The hardcoatings, system and methods disclosed herein are particularly suited for use with tools and components used in drill stings, such as drill bits, reamers, tool joints, stabilizers, drill collars, mandrels, wash pipes, mud motors, and the like, but are likewise suited for use on other tools and machine elements not associated with drilling which require protection against excessive wear. The invention also relates to hardfacing compositions comprised of laser cladding Fe—Cr alloys which contain low quantities of austenite.
2. Background of the Invention
Oil and gas wells are typically formed by rotary drilling processes that involve a drill bit connected onto the end of a drill string. Rotational motion of the drill bit in contact with the earth can create a wellbore by the earth boring action of the drill bit. The rotational motion of the drill bit can be provided by a rotary drive mechanism located at the surface that turns the drill string that in turn gives motion to the drill bit. Alternately a downhole “mud motor” can be used to convert hydraulic pressure of a circulating fluid into rotational motion of the drill bit, enabling drilling of the well without the need to turn the entire drill string.
During drilling operations, a fluid, referred to as drilling fluid or drilling mud is circulated through the drill string and up through the wellbore to the surface. The drilling fluid is used to remove the cuttings resulting from the drilling process, to reduce the occurrence of plugging of the drill bit, and can be used to cool the areas of contact between the bit and the formation that can generate heat.
In operation, downhole tools often encounter extreme conditions, including high heat, high pressure, and vibration. Additionally, these tools are subjected to rotational and sliding contact with abrasive formations, are exposed to corrosive fluids that also cause corrosion and erosion, and experience impact loading as components contact the borehole bottom and sidewalls. To protect against these conditions, particularly excessive wear, corrosion, and erosion, various surfaces of downhole tools are provided with a protective coating of hardfacing. These hardface coatings provide increased hardness to the exterior of the tool elements, particularly to the surfaces which come in contact with the abrasive formations. The required hardness is often accomplished by providing a coating composed of tungsten carbide particles which are cemented in place by a metal binder. The matrix formed by the carbide particles and the binder is applied as a coating to various exposed and vulnerable surfaces. Alternatively, a uniform coating of a hard material may be applied to an entire tool or component surface.
Conventional hardfacing materials used to provide wear resistance to the underlying substrate of the drilling tool can comprise carbides. The carbide materials are used to impart properties of wear resistance and fracture resistance to the tool. High-velocity-oxy-fuel (HVOF) tungsten carbide hardfacings containing some fraction of a metallic phase and hard chromium plating have been employed to protect these tools from wear, corrosion, and erosion. However, these hardcoatings are less than adequate in a corrosive environment because of a failure of the mechanical bond between the hardfacing (or plating) and the base metal of the tools. Often, microcracks develop from bending and thermal loading, which expose the base metal to corrosive fluid and can cause premature chipping, flaking, and fracturing of the coating. This has led to hardfacing delamination and catastrophic failure of some typical coatings.
Hardfacing is typically applied onto the underlying tool surface by conventionally known welding methods or thermal spray techniques, such as Laser Cladding, Plasma Transferred Arc or Flame Spray techniques. The process of welding the hardmetal materials onto the underlying substrate can make it difficult to provide a hardfaced layer having a consistent coating thickness, which can determine the service life of the bit.
Plasma transferred arc welding (PTAW) process has also been used to deposit a metallurgically bonded corrosion-resistant hardfacing of Hastelloy and Colmonoy on such tools. However, these hardfacing are prone to failure in either a high acidic environment containing CO2 and H2S or abrasive environment, or both. The process causes higher dilution to the base material adjacent to the hardfacing, compared to laser cladding.
Down-hole drilling tools have long suffered from abrasion wear, erosion, and corrosion, which are the limiting factors for tool life. Accordingly, there remains a need in the art for a hardfacing overlay that has improved corrosion resistance, adequate hardness for abrasion resistance, metallurgical bonding to the base metal of the drilling apparatus, dimensional stability, and little effect on mechanical properties of the base material.